Centrifugal switch



June 22, 1937. R. w. GROOT CENTRIFUGAL SWITCH Filed Sept. 7, 1934 2Sheets-Sheet 1 Inventor Robert W Go'ot, bld 77/ i @vw-M4 ttor-heg.

June 22, 1937. R. w. GROOT- CENTRIFUGAL SWITCH Filled Sept. 7, 1934 2Sheets-Sheet 2 Inventor RQbeTt VV. Groot,

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Patented June 22, 1937 v CENTRIFUGAL SWITCH Robert W; Groot, Fort Wayne,Ind., assignor to General Electric Company, a corporation of New YorkApplication September 7, 1934, Serial No. '743,110

(Cl. 20o-80) 8 Claims.

My invention relates to centrifugal switches and more particularly toimprovements in the construction of such switches.

Centrifugal switches of the so-called center contact type, wherein arotatable member carrying a centrifugally actuated contact which ismovable along the axis of rotation of the rotatable member and whichcooperates with an axially positioned stationary contact, have beenfound difficult to keep in proper operating condition, as it isnecessary for the contacts to be extremely true and smooth in order toprevent objectionable contact noise or squealing. As the contactsnaturally tend to pit or burn and become rough l5 in service, suchswitches require frequent dress'- ing of the contacts in order to givesatisfactory service. Accordingly, in my switch the contacts are mountedolf-center, with the contact surfaces in a plane perpendicular to theaxis of rotation of the rotatable member. With such a construction, theresultant windage is benecial to the action of the contacts in that itserves to cool them and to blow out arcs between them. However, in orderto adjust the setting of the switch duringY its operation, it is usuallynecessary to have an axially movable adjustable means for cooperationwith an axially positioned element on the rotatable member with theresult that wear` and some noise is produced by these adjustablemembers.

In accordance with my invention, however, I provide anovel constructionin which centrifugal force is utilized to reduce and minimize the forcebetween the stationary and the rotatable elements of the adjusting meansof the switch so` that under the normal operating speed of the switchthe pressure between the elements of the adjusting means is 'relativelyinsignificant.

An object of my invention is to provide a new and improved centrifugalsvwltch.

A further object of my ,invention is to provide a speed adjusting meansfor centrifugal switches with a centrifugal element which serves toreduce the wear in the adjusting means. My invention will be betterunderstood from the following description taken in connection with theaccompanying drawings and its scope will be pointed out in the appendedclaims.

In the drawings, in which like reference characters designate similarelements throughout the several views, Fig. 1 is a perspective view ofone embodiment of my invention; Fig. 2 is a crosssectional view of theswitch' shown in Fig. 1; Fig. 3 illustrates a modified speed adjustingmeans for a single speed switch; Fig. 4 illustrates a modified Rill S50E. 0

Way of making the electrical connections to my switch; Fig. 5 is anadditional modification showing the contact of my switch reversed;Fig.,6 is a circuit diagram illustrating an application of my switch forcontrolling the speed of a series 5 motor; Fig. 7 is a circuit diagramillustrating an application of my switch to the armature circuit of ashunt motor; Fig. 8 is a circuit diagram illustrating an application ofthe modified switch shown in Fig. 5 to the field circuit of a shunt 10motor; Fig. 9 is a perspective view of an additional modification of myswitch; and Fig. 10 is a part sectional view of the switch shown in Fig.9.

Referring now tothe drawings and more particularly to Figs. 1 and 2thereof, a shaft I, which 15 may for example be the shaft of an electricmotor whose speed is controlled by my switch, has mounted thereon arotatable member 2 which is fastened to the shaft in any suitablemanner, such as by a set screw 3. Mounted on rotatable 20 member 2 aremetal collector elements 4 and 5 which are preferably circular in shapeand which are shown as discs, although it will of course be obvious tothose skilled in the art that conventional collector ringsY may also beemployed if 25 desired. Elements 4 and 5 are insulated from the member 2and from each other by suitable insulating material, such as hard rubber6. Cooperating with the collector discs 4 and 5, respectively, arebrushes I and 8 to which the elec- 30 trlcal connections to the switchmay be made. Electrically connected to metal collector disc 4, andpreferably also supported thereby, is an offcenter ycontact 9, which asshown by way of example, is riveted to the disc 4. Supported by the 35rotatable member 2, through the medium of collector disc 5 and metalscrew studs I0, is a metal frame or plate II which may be ,made of anysuitable material, such for example, as phosphor bronze. Plate II isprovided with opposite cut- 40 away portions into which project integralfingers I2 and I3. Extensions I4 and I5 are fastened, respectively, tothe fingers I2 and I3 and these extensions have overlapping portions inthe axis l of rotation of the device. Mounted on finger I3 45 andextension I5 thereof is a contact I6 for cooperation with the contact 9.Interposed b'etween the'overlapping extensions I4 and I5 is acompression spring I'I which serves to bias the finger I3, carrying thecontact I6, in such a direction as 50 there is provided an adjustmentscrew I9 which bears against a bearing member, such as a fibre orBakelite button 20 set in the extension I4. By turning the screw I9 thecompression of the biasing spring I1 can be adjusted, thereby adjusting,in a manner to be described more in detail hereinafter, the speed atwhich the contacts of the switch open.

For relieving the force and wear of the adjusting means of the switch Iprovide another offcenter weight 2I which is fastened by suitable means,such as by riveting, to the finger I2 and plate I I-.

The operation of the switch shown in Figs. 1 and 2 is as follows: InFig. l the parts are shown in the positions they assume when the switchis at rest. If now the shaft I is rotationally accelerated thecentrifugal force on weight I8 will produce a bending movement tendingto turn the finger I3 counter-clockwise (asviewed in Fig. 2) about acenter approximately at the point where weight I8 is fastened to the armI3. This is because the centrifugal force on weight I8 is in a radialdirection passing through the center of gravity of the weight I8 and thecenter of gravity is at a distance of approximately half the thicknessof the weight I8 from its point of fastening to the arm I3. Thisdistance corresponds to the arm of the bending movement. When a certaincritical speed is reached, which speed is determined by the compressionof spring I1 and the resilience of arm I3 and the torsional resistanceof the portion of plate II to which it is integrally attached, thecentrifugal bending moment produced by the weight I8 will be sufficientto cause the contact I5 to move out of engagement with the contact 9, asis shown in Fig. 2. Consequently, an electric circuit from brush 1through discs 4, contact 9, contact I6, stud I0, disc 5 and brush 8 willbe interrupted by the separation of the contacts 9 and I 6.

At the same time that the above described action is taking place, asimilar ybending moment is being produced by the Weight 2| on the arm I2and extension I4, and this bending moment is in such a direction as tocause arm I4 to tend to compress spring I1, thereby relieving most ofthe pressure or friction between the screw I9 and the button 20. Weight2| is so proportioned that the bending moment it produces is neversurlicient to cause button 20 to leave screw I9, as this of course wouldchange the calibration or setting of the switch. The bending momentproduced by weight 2| is merely sufficient to relieve most of thepressure between button 20 and screw I9 so that wear and noise betweenthese two elements is greatly minimized.

Due to the fact that ngers I2 and I3 are inv tegral with the plate I Ithese fingers are in effect mounted on frictionless hinges and gothrough their various ranges of movement without causing any wear orlrequiring lubrication of any parts.

By screwing adjusting screw I9 inwardly the brought to rest. In thismodiiication a screw 22 is passed between extension I4 and the part ofthe plate II which is opposite thereto and a nut 23 and a locknut 24 areprovided thereon on opposite sides of the plate II. By adjusting thedistance between plate II and arm I4 the cornpression of spring I1 canbe adjusted thereby adjusting the speed setting of the switch in themanner previously described.

In the modification shown in Fig. 4, but a single collector element isemployed and current is led into the switch through the adjusting screwI9 and a metal contact member 25 which takes the place of the bre orbakelite button 20. With such a construction, the plate II is mounteddirectly on the member 2 instead of being mounted indirectly thereonthrough the interposition of the second collector element 5, as in Figs.1 and 2.

In the modication shown in Fig. 5, the contacts have been reversed, thatis to say, contact I6 is mounted on the other side of extension I5 andnger I3, and contact 9 is mounted for engagement with contact I6 bymeans of a suitable bracket 26 extending from the collector disc 4around the arm` I3 and extension I5. With this arrangement of thecontacts they are normally open and when the critical speed is attainedthe flexing of the finger I3 and extension I5 causes the engagement ofthe contacts. The modification shown in Fig. 5 may obviously be appliedeither to the switch of Figs. 1 and 2 or to the switch of Fig. 3 or 'tothe switch of Fig. 4.

In Fig. 6 a series motor 21 having a series field winding 28 iscontrolled by the switch contacts 9, I6 of the switches shown in eitherFigs. 1 and 2, or in Fig. 3 or 4. For this purpose it is preferable toconnect a regulating resistor 29 across the contacts of the switch andalso to connect a discharge capacitor 30 across the contacts forminimizing sparking thereof. With this arrangement, the contacts 9 andI5 are normally in engagement so that when the circuit including themotor 21 is energized from any suitable current source (not shown) themotor comes up to speed and as soon as the critical speedis reached thecontacts 9 and I6 open, thereby inserting the resistor 29 in series withthe motor which limits the voltage applied thereto so that the motorspeed is reduced, but as soon as it falls below the critical speed thecontacts close thereby short-circuiting the resistor 29 and the motoragain increases in speed. This action, however, is extremely rapid anddue to the inertia of the motor there are no sudden changes in speed andit operates at a substantially uniform and constant speed.

In Fig. 7 a shunt motor 3| having a shunt eld winding 32 is controlledby my switch, of the types shown in Fig. 1, 2, 3 or 4, having itscontacts 9 and I6 connected in the armature circuit of themotor. Withthis arrangement the contacts are normally closed so that the motorcomes up to speed but when the critical speed is reached the contactsopen thereby inserting the resistor 29 in the armature circuit therebyreducing the voltage on the armature with the result that the speed ofthe motor is decreased. However, as soon as the speed decreases belowthe critical value the contacts again close as has just been describedin connection with Fig. 6, and this results in holding the speed of themotor 1 substantially constant.

In Fig. 8 the shunt motor 3'I is controlled by a switch having itscontacts in circuit with the field 32. In order to control the speed ofthe motor in this manner the contacts must close on overspeed instead ofopening on overspeed and consequently a switch having contacts arrangedas in Fig. 5 must be employed. With this arrangement the contacts 9, I6are normally open, thereby causing the eld current to iiow through theresistor 9 and weakening the field of the motor. This causes the motorto tend to operate at overspeed but as soon as the critical speed isreached the contacts close thereby short-circuiting the resistor 29 and.increasing the current to the field 32 thereby reducing the motor speed.This cycle is then repeated rapidly with the result that the averagemotor speed is held constant.

In the modification shown in Figs. 9 and l0 the plate, or frame, memberII has been replaced by two frame members 33 and 34. 'Iheframe 33 isfastened to the collector disc 4 by means of screws 35 threaded intostuds 36. I have found that in some cases the hinges produced by theflexing of portions of the' plate or frame II of the. modificationsshown in Figs. 1 to 5, inclusive, became distorted and weaved at certainspeeds. In order to overcome this I have provided a relatively rigid rodor bar 3l which is mounted in slots in the studs 36, and this rod 3l isadjacent the hinge or exing portion of the frame 33 and thus preventsdistortion and weaving. As shown, the frame 33 carries the finger or armI5 for carrying the movable contact I6. Frame 33 is also provided withan extension 33 for cooperation directly with speed adjusting buttbn 20.With this construction, it is possible to eliminate entirely the helicalspring I'I of the previously described modifications and this issometimes desirable, as I have. found that at times the lhelical springtends to flutter, and thus upset the speed setting of the switch. In themodification shown in Figs. 9 and 10 the biasing spring for theadjustable contact I6 is formed bythe extension 38, the resilient hingeof the member 33 and the nger I5, all of` which elements are resilient,so that when screw I9 is turned inwardly causing button 20 to pushagainst extension 38, the biasing force on the contact I6 is increasedthereby requiring a greater speed of rotation ofthe switch for thecentrifugal weight I8 to cause contact I6 to leave the contact 9.l

I have also found that in some cases better contact action is secured ifthe contacts are placed on the opposite side of the center of the switchfrom the hinge for the movable contact, and as shown in Figs. 9 and 10,the finger I5 extends beyond the center of rotation of the switch. Withthe longer lever arm thus produced, a wider and more positive contactopening is secured.

It should also be noted that in the modification shown in Figs. 9 and 10the contacts have been reversed with respect to the collector discs orelements so that the stationary contact 9 is carried by the. smallerdisc 5 while the movable contact I6 is carried by the larger disc 4.

The resilient frictionless hinge member 34 is mounted on studs 39 bymeans of screws 40 and for bracing the hinge and preventing distortionthereof there is provided a relatively rigid rod member 4I havingeyelets through which the screws 4U are passed.

Although the arm I4 of the speed .adjusting mechanism of my switch isshown mounted on a frictionless resilient hinge in the various modifivcations of my invention which I have described,

it should be noted that such mounting is not really necessary and thatdue to the fact that the force for operating the speed adjustingmechanism, which is produced by the screw I 9, is ample to operate thismechanism regardless of any ordinary amount of friction in the hinge, itwould be entirely feasible to substitute a conventional hinge for thehinges shown in the various modifications of the speed adjusting means.

While I have shown and described particular embodiments of my invention,it will b-e obvious to those skilled in the art that changes andmodifications mayb-e made without departing from my invention, and Itherefore aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In a centrifugal switch, a rotatable member carrying a pair ofcontacts, a biasing spring for one of said contacts carried by saidmember, means for adjusting the biasing force of said springandcentrifugally actuated means carried by said member for reducing theforce of said spring on said adjusting means.'

2. In a centrifugal switch, a rotatable member carrying a pair ofcontacts, a biasing spring for one of said contacts, a movable elementcarried by said member and bearing against said spring, adjustable meansfor varying the force of said element against said spring, and acentrifugally actuated weight for varying the force. of said elementagainst said spring in the same direction as said adjustable meanswhereby the counterforce on said adjustable means is reduced inaccordance with increases in the speed of said member.

3. In a centrifugal switch, a rotatable member carrying a pair ofcontacts, a biasing spring for one of said contacts carried by saidmember, a normally stationary adjustable member cooperating with saidspring for adjusting the biasing force thereof, and centrfugallyoperated means carried by said rotatable member for reducing the forceexerted by said spring on said adjustable member in accordance withincreases in speed of said rotatable member.

4. A centrifugal switch comprising, in combination, a. rotatable member,a circular collector element mounted on said member for rotation aboutan axis perpendicular to said element, a. contact carried by saidelementv beyond the center of rotation thereof and having its contactface parallel to the plane of rotation of said element, a

` member moves said finger.

5. A` centrifugal switch comprising, in combination, a rotatable member,a pair of relatively insulated collector discs mounted thereon, acontact attached to one of said discs, a metal frame attached to theother of said discs, said frame having a cut-away portion around aninwardly extending nger, a contact carried by said nger for cooperationwith the first mentioned contact, and an off-center weight .attached tosaid finger for producing a centrifugal force in a direction to movesaid finger in response to the rotation of said member.

6. In a centrifugal switch, a rotatable member, a circular collectorelement carried thereby, an off-center contact connected to saidelement, a metal plate carried by said member, said plate havingcut-away portions around two inwardly extending lingers on said plate, ahelical compression spring between the inner ends of said fingers, acontact carried by one of said ngers for c0- operation with the rstmentioned contact, and separate centrifugal weights carried by each ofsaid fingers for urging them toward each other in response to rotationof said member.

7. In a centrifugal switch, a rotatable member, a pair of relativelyinsulated circular collector elements carried thereby, an yoff-centercontact carried by one of said elements, a metal frame carried by theother of said elements, said frame having cut-away portions aroundinwardly extending overlapping metal ngers, a compression spring betweenthe overlapping portions of said fingers, a Contact carried by one ofsaid fingers and cooperating with the rst mentioned Contact, anoff-center weight fastened to the contact Carrying lingers for producinga centrifugal force in 20 a direction to flex the contact carrying ngeragainst the compression of said spring, normally stationary means foradjusting the compression of said spring, and an off-center weightfastened to the other finger for producing a centrifugal force in adirection tending to ex the other contact linger against the compressionof said spring.

In a centrifugal switch, a rotatable member, a relatively xed Contactcarried thereby, a resilient metal frame carried by said member, saidframe having a nger carrying a movable Contact for cooperation with saidfixed contact, means adjustable along the axis of said rotatable memberfor flexing said frame and thereby adjusting the setting of said switch,and centrifugally actuated means carried by said member for reducing theforce on said adjustable means caused by the exing of said resilientframe.

ROBERT W. GROOT.

